Il rapimento di Icaro La Plume

Eva Dunkpof, the daughter of an aeronautical engineer who in the past had collaborated with Icaro La Plume in the construction of an aircraft called the "flying catamaran", kidnaps the Baron to force him to return with her to the summit of the inaccessible cliff on which the mysterious city of Ol Undas stands. La Plume, in fact, in the company of Zagor and Chico, had crashed on that peak in an adventure dating back many years before, discovering a community that had remained isolated from the rest of the world for millennia. Eva, who has hired a gang of unscrupulous men, wants to reveal the existence of Ol Undas to the scientific community and take possession of its technological secrets, inherited from antediluvian civilizations more advanced than ours. To reach the top of the cliff, a flying ship supported by balloons is built. Zagor manages to get on board, ending up returning, with La Plume, to the top of the mountain... and thus discovering what has happened to the inhabitants of the hidden city in the meantime!